1. Field of the Invention
The present invention relates to an apparatus and a method for checking the cause of defects of a semiconductor device such as an LSI.
2. Description of the Prior Art
Conventionally, the following method has been employed in order to check the cause of defects of a semiconductor device such as an LSI. First, the semiconductor device having an electric defect is broken out so that an inner semiconductor chip is exposed. Then, the semiconductor device is electrically checked by means of a semiconductor tester. The result of check is printed out and thus the defect in a circuit of the semiconductor chip is confirmed. With reference to another design drawing, a defective portion (hereinafter referred to as a defective address) on the semiconductor chip is found. As shown in FIG. 9 (a), a semiconductor chip 10' is then taken out of a package of the semiconductor device so as to be cut into a sample chip piece 20 by means of a dicing machine or the like. The sample chip piece 20 has a defective address 21 in the center thereof. As shown in FIG. 9 (b), the back of the sample chip piece 20 is abraded by means of a plane abrasive machine to a thickness of about 50 .mu.m. In FIG. 9 (b), only an abrasive table 26 of the plane abrasive machine is shown. If the thickness of the sample chip piece 20 is less than 50 .mu.m, the sample chip piece 20 may be damaged. Therefore, a charged particle beam processing apparatus is finally used. The detailed description of the above steps will be given later. In brief, with reference to FIGS. 9 (c) and (d), the abraded sample chip piece 20 is mounted on a sample supporting table (sample supporting plate) 27 which is a so-called mesh. Then, the sample supporting table 27 is fixed to the charged particle beam processing apparatus. Consequently, the sample chip piece 20 is rotated together with the sample supporting table 27. At the same time, a charged particle beam is radiated at an angle of 15.degree. to the back of the sample chip piece 20 through a round hole 271 formed in the center of the sample supporting table 27. Consequently, the center of the back of the sample chip piece 20 is made cone-shaped. The center of the sample chip piece 20 is abraded to a thickness of about 50 nm. Then, the defect of crystals in the defective address of the sample chip piece 20 is observed by means of a transmission type electron microscope so that the cause of defects of the semiconductor device is checked.
In the prior art, however, there have been pointed out the following drawbacks.
Even if the defective portion on the circuit of the semiconductor chip 10' can be confirmed by the semiconductor tester, a physical position (the defective address 21) of the semiconductor chip 10' should be specified with reference to the design drawing. This process is so complicated that the skilled often make an error.
In addition, even if the defective address 21 of the semiconductor chip 10' can be confirmed, the defective address 21 rarely corresponds to the center of the sample chip piece 20 to be observed by the transmission type electron microscope. In the cast where the semiconductor chip 10' is repeatedly formed with patterns, a great problem is especially raised. As a result, the cause of defects of the semiconductor device cannot be checked precisely.
Next, a conventional charged particle beam processing apparatus will be described in detail.
In FIG. 10, a material supporting table 127 is supported by three legs 109 and can be rotated in a direction of an arrow. The reference numeral 108 denotes screws by which the legs 109 are fixed to the material supporting table 127.
The reference numeral 120 is a material which is positioned on a material reinforcing plate 104. The reference numeral 110 denotes charged beam particles which are radiated on the material 120 obliquely.
As shown in FIG. 10 (c), scattered substances 111 adhere to a portion (a lower surface), on which the charged beam particles 110 do not directly strike, through a path 113, i.e., a path on the periphery of the material supporting table 127, or through a clearance between the material reinforcing plate 104 and the material supporting table 127. In addition, various dirt particles 112 adhere to the aforementioned portion in an atmosphere.
In other words, as shown in FIG. 11, a dirt layer 115 adheres to the back of the material to be flaked. Consequently, a portion 120' to be observed by the transmission type electron microscope is superposed on the dirt layer 115, so that the material itself cannot be observed by the transmission type electron microscope.
The charged beam is radiated in the opposite direction so that the dirt layer 115 is abraded. Consequently, the portion 120' is exposed so as to be observed by the transmission type electron microscope.
In order to confirm whether the flaked material can be observed by the transmission type electron microscope when the charged beam abrasion is completed, the following countermeasure is considered. In other words, there is provided a device for radiating light on the portion to be processed in one direction so that the light can be detected in the opposite direction. In addition, a hole is formed on the material supporting table so that the light can be transmitted. If the hole is opened, the abrasion is automatically completed.
However, the aforementioned prior art has the following drawbacks.
(1) In the case where the dirt layer adheres to a non-abraded surface, it is required to radiate the charged beam on the dirt layer to be abraded. However, the portion 120' to be observed by the transmission type electron microscope (see FIG. 11) is often abraded and removal together with the dirt layer. Consequently, a good image of the material cannot be obtained by the transmission type electron microscope.
(2) The scattered substances 111 adhere to the nonabraded surface not only through the path 113 but also through a path 114 between the material supporting table 127 and the material reinforcing plate 104 (mesh).
(3) When the charged beam abrasion is completed, it is required to detect an end point by light transmission in order to decide whether the material surface can be observed by the transmission type electron microscope. Therefore, even if it is known that the dirt is produced, a hole must be formed on the material supporting table body.